Technical Field
The present invention relates to the technical field of sludge disposal, in particular to a sludge disposal system and a method thereof.
Description of Related Art
Biological activated sludge process is the most common and mature sludge disposal technology, which has low cost in investment and operation and has a stable disposal effect. However, the biological activated sludge process has a problem, namely generating a great amount of sludge residue. The transport and disposal fees of the sludge residue take a large proportion in the total operation cost, and the disposal is limited by various conditions. At present, the disposal amount of domestic urban sludge is about 30 billion m3/a, generating about 0.2 billion m3/a of biochemical sludge with a moisture content of 98%. The yield of the sludge residue is increased by 15% each year. The annual water-contained sludge yield of a 10 million t/a oil refinery is about 10,000 ton.
Biochemical sludge residue mainly contains water, microorganisms, microbial metabolites and organic solids. Biochemical sludge residue is harmful to the environment because it has a great amount of microorganisms, viruses, parasites, organics, nitrogen and phosphorus, and odors. The biochemical sludge is voluminous because of high water content. The contained water includes free water, interstitial water, surface water and bound water. The primary cause is that the sludge has macromolecular organics with special properties. Those macromolecular organics lead to the existence of the interstitial water, surface water and bound water. The free water accounts for about 70% of the total water content, and is not attached to or bound with the sludge, thus is easy to separate, and can be separated by gravity. The water due to the effect of capillaries is difficult to separate, and needs to be separated by centrifugation or vacuuming. The surface water is bound with glue surfaces through hydrogen bonds, thus is difficult to separate and can be only separated by mechanical means after being processed. The bound water is bound with the sludge through chemical bonds, accounting for about 4% of the total water content. The bound water is very difficult to separate by common physical and chemical methods, and is a main ingredient of dehydrogenated sludge. Internal water is the water in cells, which is small in volume, but more difficult to remove.
Disposal methods of the sludge residue include landfill, soil improvement and dry-burning. The sludge residue may include a great amount of heavy metals, pathogenic microorganisms and persistently non-biodegradable organic contaminants. Soil improvement has been forbidden in some countries, while landfill and dry-burning disposal also face limits due to the increasingly insufficient land resources and strict environmental laws and regulations.
Existing biochemical sludge disposal processes include the following. Dehydrogenation: The water content is usually reduced to 80%-84%; a great amount of sludge residue still exists; and the amount of the contaminants is not reduced. Burning: Reduction is desirable, but there are problems of high cost of investment and operation, complicated operation, generation of ashes, and difficulties in smog disposal. Digestion is low in disposal cost, but only a part of the organics can be removed, and the reduction of sludge is undesirable.
At present, the main indicator of sludge reduction is the water content of the sludge cakes and total yield of sludge cakes. The water content of the sludge cakes is tested according to the national standard. Ozone aeration oxidation is to introduce high-concentration ozone into a reactor. Due to the strong oxidation of the ozone, the cell walls and cell membranes of the microorganisms in the sludge are smashed, and a great amount of organic matter is released from the cells. Therefore, this method can be used to reduce the sludge and kill harmful organisms in the sludge. Usually, the ratio of the ozone dose to the sludge amount is 0.015-0.3 kg ozone/kg sludge amount. According to Japanese literature, the ratio of the ozone dose to the converted 100% sludge amount is 0.015 kg/kg sludge amount. According to studies made by domestic universities, the ratio is 0.05-0.35 kg/kg sludge amount. Usually, the ozone and the sludge contact each other in a contactor. The ozone with such a high dose can exist in the lab stage, but is rarely achieved in the industrial stage.
For a sludge disposal factory with a daily sludge cake of 40 ton, the converted 100% sludge amount is 8,000 kg each day if calculated on the basis of 80% water content of the sludge cake, a 16.67 kg/h ozone generator is required if calculated on the basis of 0.05 kg ozone/kg sludge amount, and a 116.7 kg ozone generator is required if calculated on the basis of 0.35 kg ozone/kg sludge amount. At present, a power of 15-21 KWh is required for every 1 kg of ozone according to domestic and overseas indexes, and 8 KWh power consumption is needed even if industrial oxygen is used as a raw material to replace air. A 16 kg/h ozone generator itself has power consumption of 240-336 KWh. The equipment investment, power system configuration and operation cost are essential factors that the sludge disposal property owner must consider.
Therefore, the sludge disposal system for disposal of sludge in the prior art has the following defects: short pause time of ozone in the reactor, insufficient contact between sludge and ozone, low ozone utilization rate, high ozone dose, high power consumption, high operation cost, and difficulties in large scale promotion and application.